This invention relates to velocity change sensors.
Supplemental inflatable restraint devices that are used in automobiles are activated by velocity change sensors, sometimes called inertia switches. These sensors sense predetermined deceleration characteristics and provide switch closure signals to the devices when such predetermined characteristics are sensed. The predetermined deceleration characteristic that creates switch closure is a function of both the magnitude of deceleration and its duration. The ability of a sensor to sense a predetermined deceleration characteristic is determined by the sensor design. In order to embody this design in production switches, manufacturing tolerances must be closely controlled.
One known type of velocity change sensor that is used with supplemental inflatable restraint devices comprises a sphere that travels within a tube. The predetermined deceleration characteristic that will activate the switch is a function of several parameters. One of these parameters is the closeness of the fit of the sphere within the tube. Controlling the accuracy of this fit in production switches is a significant portion of the switch cost.
The present invention relates to a velocity change sensor which does not utilize the tube and sphere construction and for that reason offers the potential for reducing costs associated with the production of velocity change sensors for supplemental inflatable restraints while still attaining a specified degree of accuracy in such sensors.
Rather than executing linear displacement of a sphere within a tube, a sensor of the present invention comprises a sensing mass that is mounted for swinging motion in response to certain velocity changes. Several embodiments of the invention are disclosed, and they present various means for imparting dampening to the sensor operation for the purpose of discriminating between those velocity changes that should produce switch actuation and those that should not.
The features, advantages, and benefits of the invention will be seen from the following detailed description which is accompanied by drawings. A preferred embodiment according to the best mode presently contemplated for carrying out the invention is disclosed.